Apparatus for changing the moisture content of a material by the action of air



March 25, 1969 P. J. MOLLER 3,

APPARATUS FOR CHANGING THE MOISTURE CONTENT OF A MATERIAL BY THE ACTION OF AIR Filed April 18, 1967 United States Patent Int. Cl. F2 6b 21/08, 21/02 US. Cl. 34-46 3 Claims ABSTRACT OF THE DISCLOSURE Apparatus for changing the moisture content of a material by the action of air, in which the material is contained in a closed chamber which is operatively associated with a ventilator and a throttle valve by which air may be recycled or outside air may be supplied to the closed chamber. The opening and closing of the throttle valve and the adjustment of the vintilator is controlled by a control assembly adapted to measure at a given instant the ditference between the moisture content of the material to be treated and the desired moisture content and to emit control impulses corresponding to the measured dilference. A sensing device for the dew point of the outside air is coupled to the control assembly for discontinuing suction when the dew point of the air relative to the equilibrium moisture of the material reaches a value at which the air is unable to change the moisture content of the material in the desired direction at any given time.

This invention relates to apparatus for changing the moisture content of a material by subjecting it to the action of air.

It has been found that in the drying of tiles, timber or food, such as sausages, it is diificult to obtain a completely uniformly proceding drying process, which may be affected by the temperature and moisture of the supplied air and by the initial condition of the materials to be dried. It is an object of the present invention to provide apparatus which results in a more uniformly proceeding process which can be controlled so as to obtain the desired properties in the dried material. The apparatus may also be employed for wetting a material to which moisture is to be supplied in a specific manner in order to produce the desired properties in the finished product.

These objects are achieved according to the invention by supplying air to the material in an amount which is so controlled that the chronological course of the change in the moisture content of the material follows a predetermined pattern. In this manner it is possible to ensure that the drying or wetting takes place at the rate and with the effectiveness which is most advantageous at any given stage of the treatment. In addition, the process may be speeded up at any point where such action does not atfect the quality of the material, since the drying or wetting may be controlled to take place at increased speed during periods where the material will not sulTer. With materials which are very moist or quite wet, for instance, vigorous drying may be employed as long as there is a large amount of moisture to be removed, whereas the drying must be more gentle as soon as the moisture content of the material is at a low level. 'By systematically testing the material to be dried it will always be possible to determine the course of progress by which the most expedient and also the fastest drying can be achieved without any de leterious effect upon the material.

The instantaneous moisture content of the material may be determined in several ways, but according to the invention it will be convenient to determine it either by 3,434,223 Patented Mar. 25, 1969 weighing or by measuring the conductivity or the dielectric constant of the material. In cases where the original moisture content of the material is known quite exactly and no specific measuring is required to ascertain this value, it may be expedient to control the instantaneous moisture content by measuring the moisture supplied to or removed from the chamber where the material is located.

A further manner by which the instantaneous moisture content of the material can be determined in a simple manner is the employment of an evaporimeter which is started simultaneously with the drying process and which may also be adapted to automatically control the process. In cases where the moisture content of the available air ditfers substantially with respect to the material to be treated, it may be sufiicient, at any rate in periods, to recycle the air, and this may expediently be done by controlling the instantaneous moisture content of the material by measuring the instantaneous moisture content of the circulating air and adjusting the amount of air circulated per unit of time to the measured moisture content of the air.

A system according to the invention comprises a chamber containing the material to be treated and provided with a ventilator and/or a throttle valve for recycling the air, for supplying indoor or outdoor air to the chamber, while starting and stopping the ventilator. The opening and closing of the throttle valve and/ or the adjustment of the ventilator and/or the throttle valve are controlled by an assembly which is adapted to measure at a given time the difference between the instantaneous moisture content of the material, or a property of the material dependent on that content, and the desired moisture content or specific property dependent thereon, and to emit control impulses corresponding to the measured difference. In this manner the supply of air can be controlled completely and the desired course of the drying or wetting process achieved.

Air which is sucked in from the atmosphere may have a moisture content relative to the equilibrium moisture of the material to be dried or wetted such that the process does not proceed as desired, and in that case it will be expedient to provide the system with a sensing device which is adapted and disposed to register the dew point of the air sucked into the system and which is coupled to operating means for suspending the air suction when the dew point of the air relative to the equilibrium moisture of the material reaches a value at which the air is unable to essentially change the moisture content of the material in the desired direction, in which case the process is virtually discontinued.

In cases where the required air must have a temperature deviating from the temperature of the air outside the drying or wetting chamber, the said assembly may expediently be adapted to control an air heating or cooling unit mounted in the air supply duct, whereby it will be possible to employ air having a moisture content other than that of the air which might have been used directly, and thus the possibilities of providing the most effective, rapid and gentle drying or wetting process are increased.

In places where the available :air has a very stable temperature and moisture content and also where the drying of the material to be treated is desired to proceed steadily, the adjustment of the ventilator and the throttle valve relative to the measured values may be effected by means of an adjustable clockwork determining the length of the alternating active and inactive periods.

The invention will be explained hereafter with reference to the drawing, which presents a schematic view of a system according to the invention.

The drawing shows an insulated chamber 1 provided with a scale 2 with a lever 3 from which is suspended a carrier 4 supporting the material 5 the moisture content of which is to be changed.

The chamber 1 has an air supply duct 6 and an outlet 7 which communicate through a throttle valve *8, which is preferably hand operated and is adapted to either connect the two ducts directly or to connect each of them to two channels 9 and 10 respectively leading to the atmosphere. The throttle valve may also be adjusted to an intermediate position.

The scale 2 is of a type that automatically weighs and emits an impulse, for instance an electrical impulse, through a line 11 to a control assembly 12 which is adapted to compare the impulse received through the line 11 with a predetermined program for the drying or wetting process to 'be performed in the chamber 1. The difference measured by the assembly 12 is employed for providing impulses which are emitted through the line 13 leading to a ventilator 18 inserted in the duct 6. Thus the ventilator can be controlled by means of the impulses from the assembly 12 to stop or start or to change speed. To be able to adapt the air to be supplied to the system with respect to moisture and temperature, the said assembly 12 may also be connected to wetting and heating units. Through a line 14 impulses are transmitted to a wetting unit 19 which is also inserted in the duct 6, and the line leads to a heating unit 20 which is likewise located in the duct 6.

A line 17 connects the control assembly 12 with a hygrometer 21 disposed in the channel 9 which can be connected through the throttle valve 8 with the duct 6, and the impulses received from the hygrometer are passed on to the control assembly 12, where they are compared with the instantaneous moisture content of the material communicated to the assembly through the line 11, and in cases where the moisture of the air supplied to the chamber is above or below the desired value the assembly 12 will emit an impulse through a line 16 to a throttle member 22 in the channel 9 causing the throttle member 22 to block the supply of air.

From the above explanation of the method and system it will be understood that it is primarily the adjustment of the air supply which serves to control the drying or wetting process, and it is this feature which makes the entire process and the system extremely simple and reliable. Though it will in many cases be expedient to also employ the additional features explained here for controlling temperature and moisture of the supplied air, the

4 decisive feature is the adjustment of the amount of air supplied.

What is claimed is:

1. Apparatus for changing the moisture content of a material by the action of air, said apparatus comprising a closed chamber containing the material to be treated, a ventilator and a throttle valve operatively associated with said closed chamber for recycling air or for supplying outside air to the closed chamber, measuring means to measure the difference between the moisture content of the material to be treated and the desired moisture content and to emit control impulses corresponding to said measured difference, control means actuated by said measuring means for opening and closing the throttle valve and for adjusting the ventilator in response to a sensing device for registering the dew point of the outside air sucked into the apparatus, and operating members coupled to said sensing device for discontinuing suction when the dew point of the air relative to the equilibrium moisture of the material reaches a value at which the air is unable to essentially change the moisture content of the material in the desired direction at any given time.

2. Apparatus according to claim 1 comprising an air supply duct and a wetting unit in the air supply duct, said wetting unit being connected to and controlled by the control means.

3. Apparatus according to claim 1 comprising an air supply duct, a drying unit in the air supply duct, said drying unit being connected to and controlled by the control means.

References Cited UNITED STATES PATENTS 2,921,382 1/1960 Blum 34--219 XR 3,024,792 3/1962 Touton 34219 XR 1,863,943 6/1932 Rubin 3426 2,535,026 12/1950 Anderson.

2,606,372 8/1952 Foulder et a1. 3446 2,768,629 10/1956 Maul 34-46 XR 2,855,839 10/1958 Teigen 3446 XR KENNETH W. SPRAGUE, Primary Examiner.

US. Cl. X.R. 34219 

